Radioreceiver



RQ MRNHAM v AL 1,943,789

RADIORECEIVER Filed way 28, .w32

Patented Jan. 16, 1934 UNITED STATES RADIoRECEIvER Paul O. Farnham and Henry F. Argento, Boonton,

N. J., 'assignors to Radio Frequency Laboratories, Incorporated, Boonton, N. J., a corporation of New Jersey Application May 28, 1932. Serial No. 614,249,

l'l Claims.

This invention relates to radio receivers and particularly to a receiver having improved characteristics from the standpoint of selectivity.

The commercial radio receivers are characterized by a marked variation of selectivity. with frequency and, in some instances receivers which fail to provide satisfactory selectivity at the high frequency end of the present broadcast band of from 550 to 1500 kilocycles tune so sharply at .the lower frequencies as -to introduce audio distortion by cutting of the side bands. Good audio quality, particularly when separate reproducers are kemployed for the lower and higher audio frequencies, necessitates an approximately uni- 35 form transmission of a b'and of frequencies but band pass transmission or low selectivity is not possible over the entire tuning range. The general practice has therefore been to effect some compromise between the conflicting design requirements and, as a result, the selectivity of the known receivers varies with frequency and may be either too low to prevent interference between adjacent channels or too high for good tone quality. l

An object of the present invention is to provide a radio receiver in which the selectivity is under manual control and, for any setting of the manual control, is substantially constant over the tuning range. nn object is to provide a variable band 00 Width transmission system including a plurality of cascaded tuned circuits, and in which certain of the tuned circuits exhibit a substantially constant selectivity over the signal frequency range and other circuits include elements for varying the width of the transmitted band of frequencies, the transmission efliciency of the latter circuits being independentof the frequency of the received signal. A further object is to provide a superheterodyne receiver including a carrier frequency 4@amplifier which exhibitsV a constant selectivity over the entire signal frequency band, and an intermediate frequency amplifier having cascaded tuned circuits which may be manually adjusted to vary the width of theI band of frequencies `fory which the transmission efficiency is substantially constant. More specifically, an object is to provide a supe-rheterodyne' of the type stated in which theA tuned carrier frequency circuits include circuit elements for automatically introducing losses when tuned to lower frequencies, thus preventing variation of selectivity with frequency. A further speciflciobject is to .provide a coupled circuit capable of adjustment to vary the v width of the resonance curve without substantial change in the shape of the resonance curve and without change in the natural resonant frequency of the coupled circuits. More specifically, an object is to provide coupled circuits of the type last stated in which the coefficient of coupling between the circuits is so varied as to change the width of the resonance band without changing the natural resonant frequency, and the power factors of the circuits are simultaneously varied to prevent a change in the general shape of the resonance cunve. 65

These and other objects and advantages of the invention will be apparent from the following specification, when taken with the accompanying drawing, in which,

Fig. l is a circuit diagram of one embodiment of the invention,

Fig. 2 isla curve sheet showing selectivity curves for different power ratios of thecoupled circuits, and l Fig. 3 is an equivalent diagram of one pair ofA 'Z5 coupled circuits.

lin the drawing, the reference character l identies a carrier wave or radio frequency amplifier tube which precedes the rst detector 2 of a superheterodyne receiver; the beat frequency signais produced in tube 2 vby beating the carrier wave with local oscillations from the oscillator 3 being passed to the cascaded tubes fi,v 5 of an intermediate frequency ainplier, and then to the second detector 6. 85

The input system between the collector systemA AG is of the type which reduces the frequency variation of, the input system gain, and preferably this result is obtained by including, in series, between the collector A and the tuned in'- 90 put circuit of tube 1, a choke 7 which resonates with the antenna` capacity at a frequency slightly above the highest frequency to which the receiver may be tuned.

The tuned input circuit of tube' 1 comprises 95 an inductance 8 connected between the control grid and cathode, and shunted by a tuning condenser 9 in series with a parallel circuitcomprising a resistance 10 and shunt capacitydl. The coupling between the amplier tube l and detector 2 preferably 4is of the twin-circuit type, i. e., includes two circuits substantially identical with the input circuit of tube l and coupled with 4 somewhat less than critical Ishape coupling. Inductance 8 of the first twin circuit is coupled to 105 the plate coil l2 of tube l.

The high potential terminals of the twin inductances 8 are coupled by a capacity 13 and, between thel low potential terminals of each twin inductance 8 and a-common coupling capacity 14, 110

automatic losser circuits comprising a resistance l0 and condenser ll are provided. Tire tuning con.- densers 9 of the twin circuits are connected between ground and the respective high potential terminals of the twin inductances. This twin circuit, except for the addition of thenlosser elements, is substantially identical with the circuit described in the copending application of Paul O. Farnham, Serial No. 461,020, filed June 13, 1930. As described in said application, the two coupling capacities 13, lfi may be so related as to provide an approximately constant coupling between the circuits for all frequencies. The purpose of the twin circuits is, of course, to provide increasedselectivity. The several tuning condensers 9 of the carrier wave circuits and the similar tuning eondensen 9' of thel oscillator 3 are preferably mechanically connected, as indicated by broken lines l5, as is customary in sincollector structure to the input terminals of thev intermediate frequency amplier is therefore substantially constant over the entire carrier frequency band.

This condition makes it possible to obtain a uniform control, over the entire carrier frequency band, of the overall selectivity of the receiver by an appropriate design of an intermediate frequency amplifier for passing a band of frequencies of controlled width.

The intermediate frequency couplings between tubes 2 to 6 are preferably of the transformer type. The primarywindings 16 and secondary windings 17 of the several transformers are preferably identical, and each winding is tuned to the same resonant frequency by trimming condensers 18. One of the intermediate frequency transformers, as shown the transformer between the amplifier 5 and second detector 6, maybe of the usual fixed type, and only the other two transformers are designed for manual adjustment to vary the width of the resonance band.

`As indicated by the arrows 19, the magnetic coupling of the windings of the transformers associated with the tube 4 may be adjusted to vary the selectivity of thereceiver. To prevent substantial change in the shape of the resonance band as its width is varied, th'e tuned circuits of these transformers include adjustable series resistances 20, and the adjustable control elements of the variable rsistances `and variable couplings are all mechanically connected as indicated by broken lines 21, for simultaneous operation. Since the changes in the coupling between the windings of a transformer will not alter the resonant frequency of the individual windings, the natural resonant frequency of the transformer is not affected by changes in the coupling. Increasing the coupling beyond critical shape would, however, result in the production of two peaks separated by a depression which increases in magnitude with an increase in the coupling coefficient, i. e., the shape of the resonance curve would change with its width.

The variable resistances 20 prevent or reduce this variation in the shape ofthe resonance curve, and their method of operation will be apparent from a consideration of Figs. 2 and 3.

The variable transformers provide alternating current circuits, as shown in Fig. 3, which include inductance, capacity and resistance, the alternating voltage Eo impressed on the rst circuit developing a Voltage E across the condenser of the second circuit. The impedances of the coupled circuits are designated as L1, C1, R1, and as L2, C2, R2, respectively. As is well known, the relationships between the values of the several characteristics of the Fig. 3 circuit may be expressed by the following equations:

Coefficient of coupling;

Transmission emciency at w;

at wo where w may be any frequency olf resonance.

Data for selectivity curves is obtained by measuring the transmission eiciency for a particular resonance frequency and for frequencies 0E resonance, the curve being usually plotted between the transmission efiiciency and the frequencies'of resonance. An examination of such curves will show that the selectivity increases as the width of the plotted curve decreases and, for purposes of analysis, it is usual to determine the widthof the frequency band, Aw, for which a given ratio of transmission obtains. For example, if the resonant frequency is 1000 kilocycles, the selectivity of the circuit may be expressed in terms of the width of band between those frequencies, above and below 1000 kilocycles, for which the transmission eiciency is only one-half of that for 1000 kilocycles. Experience has shown thatthe width Aw of the band of equal transmission varies with the resocurves of Fig. v2. Designating the ratio of equal transmission band Width to resonant frequency as Am -wand dividing this ratio by the power factor 1, of the coupled circuits, units are obtained which may be utilized as ordinates for generalized selectivity curves for coupled circuits such as shown in Fig. 3. The three curves shown in Fig. 2 are selectivity curves for different adjustments of the Variable factors of one of the coupling circuits of the intermediate frequency amplier.

Curve A of Fig. 2 shows the selectivity of one pair of coupled circuits when the coupling M, and the ratio was substantially zero. Curve B was plotted from data obtained when the circuit was adjusted to make Vthe factor 7c equal to unity, and curve C was plotted tor an adjustment corresponding, to lc equal to two. The important fact demonstrated by these curves is that the shape of the resonance curves, or the selectivity curves, is dependent upon the resistance or power factors of the coupled circuits.

lvl. By increasing the circuit resistances R1, Rz

in the same ratio as the increase in the coupling M, 4the selectivity is still represented by the curve B but the width of this curve is increased since the ordinates 1l are proportionately decreased by the increase in y the power factor The width of the resonance curve is thereby increased but its shape remains unchanged,

When the power factors of the circuits ,and theirV coupling are varied simultaneously and at the same rate, all of the intermediate frequency .i depression will be compensated if another circuit is continuously operated to provide the selectivity represented by single peak curve B.

The invention therefore provides a. transmission system or radiol receiver that may be ytuned over a band of frequencies, andwhich has the novel characteristic of a controlled selectivity which, for any given adjustment, is constant over the frequency band. The selectivity may be increased ,or decreased at will according to the particular conditions existing ,at thevtimo signals are width transmission circuits.

does not affect the tuning of the receiver as the being received. When the signals are of such 'magnitude as to exclude interference from adjacent channels and to swamp out static, the receiver may be adjusted for `low selectivity, i. e., to pass a. relatively wide band of frequencies with approximately uniform'A transmission, thus ensuring good tone quality. If the receiver is tuned to another and comparatively weak signal, or if the existing conditions outside the receiver so change as to result in interference or noise in the reproduction of the same signal, the selectiv` ity may be increased to eliminate the disturbing factors by an appropriate adjustment of the couplings and resistances of the variable band- This adjustment variable transmission circuits have the same natural resonance frequency for all adjustments. The invention isY applicable to other types of transmission circuits, either tuned'to a single 95` frequency or tunable over a band, and the selectivity adjustment may be continuously variable or variable by set incre ents. The invention is not restricted to .the particular circuit arrangement herein shown and described, as many changes in the circuit elements, their relative arrangements and magnitudes fall within the spirit of our invention as set forth in the following claims.

We claim:

l. In a transmission system, the combination with a pair or tuned circuits, and a reactive coupling between said circuits, of means for simultaneously controlling both the shape and the width of the selectivity curve ofv said circuits without altering the natural resonant frequency thereof.

2. In a 'transmission system, the combination with a pair o f tuned circuits, and reactive coupling between said circuits, of means for ennuitaneously changing the magnitude of the coupling betweensaid circuits .and theresistances of said circuits, thereby to control both the width and the shape ofthe selectivity curve of saidi circuits.

3. In Latransmission system the combination 121 with two`tuned circuitseach including adjustable resistance, and magnetic coupling between said circuits, of means for simultaneously adjusting the lcoupling between said circuits and the effective magnitudes of the said resistances.

' 4. The invention as set forth in claim 3, wherein said means adjusts the coupling and the resistances at suchrelative rates that the shape of the selectivity curve'of said circuits remains constant `as its width is altered 'by Variation of said cou- 1m pling.

45. In a tunable system for the transmission of signals falling within a band of frequencies, the,` combination with a tuned amplifier having a substantially constant selectivity forv theI entire frequency band, of means adjustable at will to determine the band width of over-al1 transmission of the system, said means comprising'a second tuned amplifier, and means manually adjustable at will during operation of the receiver to determine the selectivity of the said second amplier. i

6. The invention as set forth in claim 5, wherein said first amplifier is a radio frequency amplifier tunable over a band of frequencies, and said second amplifier is an intermediate frequency amplifier tuned to a fixed frequency".`

'1. `In a tunable 'system for the transmission of modulated signals falling within a band ofv carrier frequencies, the combination with a car- '150 rier wave amplier including a plurality of tunable circuits having a substantially constant selectivity over the entire carrier :frequency band, of a second ampliiier including a plurality of circuits tuned to resonate at a xed frequency, means 'for adjusting the bandwidth of transmission of said second amplifier, and means adjustable simultaneously with said first means to maintain said second plurality of circuits in resonance at said fixed frequency for all adjustments of said rst means.

ii. A carrier wave receiver of the type tunable over a band of frequencies and including a plurality of cascaded tubes coupled by tuned circuits, and adjustable impedances in certain of said circuits for determining the overall selectivity of said receiver, characterized by the fact that a plurality of said adjustable impedances are simultaneously adjustable to maintain the overall selectivity constant throughout the tuning range of said receiver.

9. In a carrier wave receiver tunable over a band of frequencies, the combination with a plurality of amplier tubes coupled in cascade by resonant circuits, of means adjustable to determine the overall selectivity of the receiver, and means substantially preventing variation of selectivity with frequency throughout the range of selectivity adjustment afforded by said adjustable means.

l0. In a carrier Wave receiver, a plurality of cascaded amplifiers and couplings between adjacent amplilers, the coupling between one pair of adjacent stages comprising a pair of circuits tuned to the frequency of a desired signal, reactance coupling said circuits to each other, and means for adjusting the width of the selectivity curve of said coupled circuits without change in the shape of said curve;

ll. ln a carrier wave receiver, a plurality of cascaded stages and couplings between adjacent stages, the coupling between one pair of adjacent ampliiiers comprising a pair of circuits tuned to the frequency of a desired signal, reactance coupling said circuits to each other, adjustable resistances in each of said circuits, and means for adjusting the eective magnitudes of the said resistances and of said coupling reactance. i

l2. In a tuned carrier wave receiver, a plurality of cascaded coupling circuits having an overyall transmission efficiency corresponding to not more than critical shape coupling, certa'n of said coupling circuits including a pair of reactively coupled circuits, means for adjusting the magnitude of the reactive coupling between said pair of circuits, and means operable throughout the range oi adjustment of the magnitude of the said reactive coupling for maintaining the overall transmission emciency Within values corresponding to not more than critical shape coupling.

13. ln a tuned carrier wave receiver, the'combnation of a pair of vacuum tubes, an output circuit for one tube, a tuned input circuit for the second tube, reactance coupling said circuits in a degree corresponding to approximately but not in excess of critical shape coupling, adjustable means for increasing the magnitude of said coupling reactance, and means adjustable simultaneously therewith for maintaining the coupling between said circuits at less than critical shape coupling.

14. In a carrier wave receiver tunable over a band of frequencies, a plurality of stages tuned to the same frequency and each having a selectivity not in excess of critical shape coupling, means including an adjustable impedance for decreasing the selectivity of one of said stages, and adjustable means for preventing said decrease in selectivity from decreasing the overall selectivity of said cascaded stages to less than that corresponding to critical shape coupling, said means being simultaneously adjustable at the will of the operator of the receiver.

l5. The invention as set forth in claim 14, wherein sa'd last means prevents the selectivity of Vthe stage of decreased selectivity from decreasing to less than that corresponding to critical shape coupling..

16. In a transmission system, the combination with a tuned carrier wave amplier having an approximately constant selectivity over the entire frequency band, of means for adjusting the overall selectivity of said system to* different values which remain constant over the entire frequency band to which said carrier Wave amplifier may be tuned, said means including a second amplier, and means for adjusting the selectivity of said second amplifier and the shape of the selectivity curve thereof.

17. The invention as set forth in claim 16, wherein said second amplier includes a pair of circuits coupled by a reactance and each circuit includes an adjustable resistance, and said last means comprises means for simultaneously varying the magnitude of said reactance and said resistances.

PAUL O. FARNHAM. HENRY F. ARGENTO.

reactance.

1,943,789.-Paul 0. Farnham and Henry F. Argento, Boonton, N. J. RADfonEcEIvER. Patent dated January 16, 1934. Disclaimer filed January. 18, 1935, by the assignee,Radz'o Ucrporatt'on' of America. y Hereby enters this disclaimer to the said claims of said Letters Patentvvhich are in the following Words, to witg" j f 1. In a transmission system, the combination with a pair of tuned circuits, and a reactive coupling between said circuits, of means for simultaneously controlling both the shape and the width of the selectivity curve oflsaid circuits Without altering the natural resonant frequency'v thereof. 3. In a transmission system the combination with two tuned circuits each including adjustable resistance, and magnetic coupling between said circuits, of

means for simultaneously adjusting the coupling between said circuits and the effective magnitudes of the said resistances. l

8. A carrler Wave receiver of the typetunable over a band of fre 'uencles ,and including a' plurality of cascaded tubes coupled'by tuned circuits, an adjustable impedances in certain of said circuits for determining the overall 4selectivlty of said receiver, characterized by the fact that a plurality of said adjustable impedances are simultaneously adjustable to maintain the overall ,selectivity constant throughout the tuning range of said receiver.

11. In a carrier Wave receiver, a plurality yof cascaded stages and couplings between adjacent stages, the coupling between one pair of adjacent ampliierscomprising a pair of circuits tuned to the frequency of a desired signal, reactance coupling said circuits to each other, adjustable resistances in each of said circuits, and means for adjusting the electivemagntudes of the said resistances and of said coupling [Oficial Gazette February 2, 1935.] 

